The invention relates generally to a heating oven for drying and curing objects therein. More particularly, the invention concerns a combined radiant and convection heating oven for such applications as drying of painted objects.
It is known in the paint finishing art to dry and cure paint coatings on objects, such as automobile body parts, by subjecting the objects to both convection zones and radiation heat zones in a paint baking oven. Furthermore, it has been previously suggested that the benefits of convection and radiant heating may be advantageously combined in the same area of an oven. For example, see Radiant Convection Heating, A Marriage Of Two Systems, by Henry J. Bennett, Industrial Gas, February 1976. The Bennett reference suggests the combination of convection heating and infra-red radiant heating to combine the benefits of both and to cancel out the drawbacks of each in a combination called "radiant-convection heating". In such a combination, Bennett suggested that the benefits of convection heating (uniformity of temperature profile over the surface of the object being baked) and infra-red radiant heating (speed) may be used to cancel out each other's drawbacks when used in combination.
U.S. Pat. No. 4,785,552 to Best discloses a convection stabilized radiant oven wherein the ambient temperature of the oven air and the temperature of the radiant walls in the oven chamber are both controlled. The '552 patent discloses a baffle plate arrangement in one embodiment and turbulating fans in another in a combustion chamber immediately behind the radiant emitter walls of the oven for supplying heat to the radiation emitting surfaces.
U.S. Pat. No. 5,230,161 to Best discloses a radiant wall structure for use in a paint baking oven with a combustion chamber abutting the radiant wall and having a cross-sectional area or distance between the walls of the combustion chamber varying as one proceeds from the bottom of the oven to the top thereof.
Prior art radiant ovens are additionally known which feature longitudinally extending radiant heating ducts abutting the radiant surfaces, but the ducts are not truly independently controllable, in that they are conventionally interconnected in serpentine fashion thereby providing, as does the Best '552 and '161 patents, unitary heating chambers behind the radiant surfaces.
There is therefore seen to be a need for a combined radiant and convection heating oven wherein the temperature of the object being baked may be controlled by holding the ambient air temperature in the oven substantially constant while varying the convective heat transfer coefficient--i.e. the rate at which heat is transferred from the convection air to the surface of the object--by varying the air flow volume of the convection air impinging upon the object being dried. There is also seen to be a need for controlling the temperature profile of the radiant surfaces in such an oven by providing for a plurality of independent radiation panels, each panel having its own heating duct which can be independently regulated to a predetermined temperature. Finally, there is seen to be a need for a combined radiant and convection oven wherein the radiating surfaces may establish a predetermined temperature profile over a longitudinal length of the oven as well as the height of the baking chamber thereof by, for example, varying the cross-sectional area of the heating ducts associated with such radiation panel to vary the air flow rate or other heating gas flow rate therethrough.